Adjectives decline according to the grammatical gender and number of the nouns they modify.
hvid - singular common gender.
hvidt - singular neuter gender.
hvide - plural of either gender.
hvide is also used when applied attributively (in front of) a definite noun, as in “det hvide brød”.
We are told elsewhere that a definite object (brødet - the bread - here) takes the plural form of the colour name - which would be hvide here, but this is not the case - or have I got the wrong end of the loaf?
I understood that what you say is for the definite way (det hvide brod). here it's used with "er", so it is an attribute (at least, we call it that way in French). With "er" it's the simple way (common or neutral).